Hybrid Hall Effect Magnetoelectronic Gate

ABSTRACT

Hybrid Hall Effect Devices implemented with Spin Transfer Torque write capability are configured as magnetoelectronic (ME) devices. These devices are useable as circuit building blocks in reconfigurable processing systems, including as logic circuits, non-volatile switches and memory cells.

RELATED APPLICATION DATA

The present application claims priority to and is a continuation-in-partof Ser. No. 14/703,006 now U.S. Pat. No. 9,432,021 and Ser. No.15/219,928 both of which are continuations of Ser. No. 14/133,055 nowU.S. Pat. No. 9,024,656, which in turn claims the benefit under 35U.S.C. §119(e) of the priority date of Provisional Application Ser. No.61/739,757 filed Dec. 20, 2012, all of which are hereby incorporated byreference. The present application is also related to Ser. No. xxxxxxxxfiled on the present date, attorney docket number MJ 2016-CIP2 and whichis also incorporated by reference herein.

STATEMENT AS TO GOVERNMENT RIGHTS

This application is a continuation in part and claims priority to anapplication that was filed during a time when the inventor was employedby the Naval Research Laboratory as part of Task Area MA02-01-46, WorkUnit T042-97, and was developed as a result of efforts associated withNRF grants funded by MEST (2010-0000506, 2011-0012386 and 2012-0005631),the industrial strategic technology development program funded by MKE(KI002182), the Dream project, MEST (2012K001280), GRL and the Office ofNaval Research. To the extent they are not otherwise alienated,disclaimed or waived, the government may have certain limited rights touse, practice or otherwise exploit some or all portions of theinventions herein.

FIELD OF THE INVENTION

The present invention relates to non-volatile logic and memoryelements/circuits, and particularly composite circuits using bothmagnetoelectronic and semiconductor devices. The invention hasparticular relevance to methods and circuits that perform informationprocessing with very low power consumption.

BACKGROUND

The following references are also incorporated by reference herein:

-   -   Mark Johnson, U.S. Pat. No. 5,652,445 (July, 1997).    -   Mark Johnson, U.S. Pat. No. 6,140,838 (October, 2000).    -   Mark Johnson, B. R. Bennett, P. R. Hammar and M. M. Miller,        “Magnetoelectronic Latching Boolean Gate,” Solid-State        Electronics 44, 1099 (2000).    -   Sungjung Joo, Mark Johnson, et al., “Magnetic Field Controlled        Reconfigurable Semiconductor Logic,” Nature 494, 72-75 (2013).    -   Mark Johnson, “Magnetic Logic: Fundamentals, Devices, and        Applications,” Wiley Encyclopedia of Electrical and Electronics        Engineering, ed. John Webster, (John Wiley and Sons, Inc.,        Hoboken, N.J., 2015).    -   Mark Johnson, U.S. Pat. No. 9,024,656 (May, 2015).

U.S. Pat. No. 9,024,656 by the present inventor (incorporated byreference herein), describes a system and method for performing lowpower logic operations. Whereas logic operation performed withtraditional semiconductor technology relies on periodic synchronizedpulses from a clock, operation of the low power technique usesindividual pulses. In the former case, the logic system is constantlypowered on. In the latter case, the quiescent state of the system isoff. Power is applied only during the brief intervals when individualpulses are required. At all other times, the system draws no power. In'656, this novel kind of digital logic processing is called nonvolatilelogic.

The invention described in '656 was motivated by the development of anovel device, the magnetic field controlled avalanche diode (MFCAD). TheMFCAD is described in the article (Nature, 2013) and in U.S. Pat. No.9,331,266 B2 (Joonyeon Chang, Mark Johnson et al., “Magnetic FieldControlled Reconfigurable Semiconductor Logic Device and Method forControlling Same”). This device can behave as a nonvolatilereconfigurable Boolean logic cell. Patent '656 showed how thereconfigurable cell could be used for constructing logic buildingblocks, including as an Arithmetic Logic Unit (ALU) that performs binaryio logic operations. The patent then developed and presented anarchitecture for a nonvolatile digital logic and signal processingsystem. Dramatic power savings can be achieved because the normaloperational state is “off.” When an operation is required, individualpulses are applied and, when the operation is complete, the results arestored in nonvolatile memory and the system returns to the quiescent,zero power condition.

The magnetic field controlled avalanche diode is a type ofmagnetoelectronic device where the output is an electric current. Mostmagnetoelectronic devices, for example the spin valve (SV) and themagnetic tunnel junction (MTJ), are magnetoresistors. They behave asvariable resistors with bistable LOW and HIGH resistance values that areassociated with binary 0 and 1. The resistance state is a function ofthe magnetization orientation of one (the free ferromagnetic layer) oftwo ferromagnetic layers in the SV or MTJ. The resistance state can beset (i.e. written) using a magnetic field to set a magnetizationorientation state. For integrated devices, the magnetic field isassociated with an electric current. The write current may be appliedthrough an inductively coupled write wire and produces a local magneticfield. Alternatively, the write current may be a spin polarized currentinjected directly into the ferromagnetic layer. The resistance state ofthe magnetoresistor then is sensed (i.e. read out) by applying a biasand measuring the resistance. The resistance state of the SV and MTJ isdetected by electric transport properties associated with a spinpolarized current that transits both ferromagnetic layers. Becausemagnetoresistors typically have a large resistance value, the bias iscommonly a current and the output is read out is a voltage.

Thus, a typical magnetoelectronic device has current input and voltageoutput. These characteristics are ideal for nonvolatile memory but areproblematic for logic. Digital logical processing requires multipleoperations. One gate is linked to subsequent gates by fanout, with theoutput of one gate providing the input to one or more subsequent gates.Fanout requires that device output preferably should be a reliable andreproducible current source.

In the MFCAD, the channel of an avalanche diode has resistance valuesthat depend on the orientation of an applied magnetic field. The diodetypically is biased by a voltage and the output is a current thatdepends on the magnetic field. The MFCAD differs from the SV and MTJbecause detecting the output does not involve spin polarized currentflowing in the channel of the device. For the integrated MFCAD, theexternal magnetic field is provided as a local fringe magnetic fieldnear the ends of one or more patterned ferromagnetic elements. Themagnetization states of the ferromagnetic elements, and therefore thelocally applied fields, are bistable and nonvolatile.

Thus, the MFCAD is characterized as a device with bistable magnetizationconfigurations that are set by applying an input write current topatterned ferromagnetic elements in the MFCAD device cell. For read out,the diode channel is biased with a voltage to give an output in the formof a current, with bistable output current values that depend on thelocally applied magnetic field, and therefore depend on themagnetization configuration of the ferromagnetic elements. As such, itis well suited for use in circuits with other MFCADs, or with othermagnetoelectronic devices, where the input is required to be a current.A disadvantage of the MFCAD is that while it is a promising device, itis in an early stage of research and development and has not beencommercialized.

The MFCAD has demonstrated basic reconfigurable functions. As describedin (Nature, 2013) and '266, one embodiment of an MFCAD reconfigurablecell can be reconfigured to perform an AND or OR function. A differentembodiment can be reconfigured to perform a NAND or NOR function. Thearchitecture described in '656 is general and works for an ALU that canbe reconfigured to perform more than two Boolean functions. However, theexample presented in '656 involved an ALU that could be reconfigured toperform two functions, the AND or OR function.

SUMMARY OF THE INVENTION

An object of the present invention, therefore, is to overcome theaforementioned limitations of the prior art.

An object of the present invention therefore is to overcome some of thelimitations of existing MFCAD structures by developing ALUs that involveother magnetoelectronic devices, including specifically a suitableHybrid Hall Effect (HHE) device. A further objective is to develop ALUscomprising composite sub-circuits that include a magnetoelectronicdevice along with one or several semiconductor transistors.

Another object of the present invention is to provide an improved HHEdevice cell that can operate as the ALU that is used in the nonvolatilelogic architecture of '656. Equivalently stated, this shows that thenonvolatile architecture of '656 can be implemented using an appropriateHHE cell.

Another object of the invention is to provide a composite HHE cell thathas CMOS level outputs, which thereby offers further significantimprovement.

A further object of the invention is to show that simple combinations ofthe composite HHE device cells can operate as the ALU and performreconfigurable functions of AND, OR, NAND, NOR and XOR. Therefore theimproved composite HHE cell expands the utility of the ALU and therebyoffers significant advantages. A further object of the invention is toshow how a magnetoelectronic device, the HHE, can be used in combinationwith one or more CMOS FETs to form a cell that behaves as an appropriatenonvolatile switch.

Still a further object of the invention is to show how amagnetoelectronic device, the HHE, can be used with a small number ofCMOS FETs to form a memory cell. The sub-circuit for this cell is nearlyidentical with the nonvolatile reconfigurable Boolean logic cell that isused as the ALU.

Furthermore, a final object of the invention is to show that this NVmemory cell can be used with CMOS logic sub-circuits and circuits. Whenused at the output stage, this NV memory cell can store the results ofan operation. The sub-circuit or circuit then can be powered down untilthe result is needed at a later time. The result then can be recalled inthe form of a CMOS compatible binary pulse.

It will be understood from the Detailed Description that the inventionscan be implemented in a multitude of different embodiments. Furthermore,it will be readily appreciated by skilled artisans that such differentembodiments will likely include only one or more of the aforementionedobjects of the present inventions.

Thus, the absence of one or more of such characteristics in anyparticular embodiment should not be construed as limiting the scope ofthe present inventions.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a preferred embodiment of areconfigurable non-volatile logic unit implemented in accordance withthe teachings of the '656 patent;

FIG. 2A is a schematic description of a circuit symbol that represents aprior art HHE device as shown in the '838 patent;

FIG. 2B is an embodiment of a variant of an HHE device that has invertedinputs;

FIG. 2C is a perspective sketch of an improved HHE device embodimentimplemented in accordance with the present teachings, showing aferromagnetic layer of the HHE device, and supportingstructures/components used to apply a Spin Torque Transfer (STT) input;

FIG. 2D is another perspective sketch of the of the improved HHE deviceembodiment of the present disclosure that has an STT input;

FIG. 3A is an embodiment of a reconfigurable composite logic cellcomposed of two improved HHE devices (FIG. 2D) and having a simple CMOSinverter;

FIG. 3B is a truth table for the reconfigurable cell of FIG. 3Aillustrating that the cell can perform the Boolean functions: AND, OR,NAND, NOR, XOR.

FIG. 3C is an embodiment of an ALU, using an improved HHE device cellsuch as shown in FIG. 2C, and which is suitable for use in thenonvolatile logic architecture of '656;

FIG. 4A is an embodiment of a reconfigurable composite logic cellcomposed of a single improved HHE device, with inverted inputs (FIG.2B), and a CMOS inverter which performs the functions AND/OR; anoninverting CMOS buffer would perform the functions NAND/NOR.

FIG. 4B is an embodiment of a reconfigurable composite logic cellcomposed of a single improved HHE device (FIG. 2D) and a CMOS bufferamplifier which performs the functions AND/OR; a cell with invertingCMOS amplifier would perform the functions NAND/NOR.

FIG. 5 is an embodiment of a nonvolatile switch composed of a singleimproved HHE device (FIG. 2D) and a single field effect transistor(FET).

FIG. 6A is an embodiment of a composite nonvolatile memory cell composedof a single improved HHE device (FIG. 2D) and a CMOS buffer amplifier.

FIG. 6B shows a circuit symbol representing a nonvolatile memory cell.

FIG. 7 is an embodiment of an improved semiconductor logic circuit, ahalf adder, which includes 2 nonvolatile memory cells of the type shownin FIG. 6A.

DETAILED DESCRIPTION

The devices, circuits and logic units described in this invention haveimportant advantages. Several embodiments are reconfigurable to performmultiple Boolean operations, such as AND, OR, NAND, NOR, XOR and XNOR.All embodiments preferably have output levels where LOW is essentiallyzero and HIGH is a positive voltage. The HIGH output voltage typicallyis high enough to provide output as a current. Such levels are readilysensed and then associated with binary “0” and “1.” This is an advantageover the MFCAD where LOW output is not exactly zero. Furthermore, thisis an advantage over magnetoresistive devices where a LOW output is alsonot exactly zero.

Furthermore, several embodiments disclosed herein provide outputvoltages at calibrated semiconductor CMOS levels V_(DD) and V_(SS). Suchlevels are appropriate for integration with traditional semiconductordigital electronic (SDE) devices. Furthermore, these levels can beeasily converted in turn to current pulses with amplitudes that aresufficient to provide output from one stage to input at one or moresubsequent reconfigurable magnetoelectronic cells/circuit stages.

The main embodiment discussed below is an improved HHE device which canbe employed in a new type of magnetoelectronic cell. This cell can beconfigured for many purposes, including to operate as the ALU that isused in the nonvolatile logic architecture of '656 and performreconfigurable functions of AND, OR, NAND, NOR.

In addition, patent '656 employs several “nonvolatile pass switches” (NVpass switch). For example, such a switch is used to open or close accessto a data bus or address bus. The devices described here, in combinationwith one or more CMOS FETs, can form a cell that behaves as anappropriate nonvolatile switch.

The '656 patent also employs several nonvolatile memory cells (NVmemory). For example, such a cell is used as a test register at theoutput stage of the ALU, and such cells are used as registers at thedata input ports. The devices described herein can be implemented assuch form of memory cell.

FIG. 1 presents a symbolic description of a generic ALU 100 that iscentral to the architecture of '656. The operation of this ALU issummarized here to better understand the context of the innovations ofthe present disclosure. As stated in the Background, the ALU in '656 wasbased on a preferred embodiment in which a MFCAD is used as thepreferred reconfigurable logic element. A pulse applied to terminal C102 configures or determines the Boolean function A?B (AND or OR; NANDor NOR). At a later time, input pulses applied to terminals A 104 and B106 (pulses to A and B are synchronous, but the pulse to C occurs at anyprior time) result in a configuration of the magnetization orientationsof ferromagnetic elements that provide local fields to the avalanchediode. These fields set/determine the output current of the diode. Atany later time, a readout voltage pulse applied to terminal D 108results in a current through the diode. The current has stable LOW(binary 0) or HIGH (binary 1) values representing the result of theselected Boolean operation on input A, B.

In FIG. 1, the “result stored” box 122 has the following meaning. Onceinputs C, A and B are applied, the reconfigurable device in the ALU isin a nonvolatile configuration (retains a logic state) that representsthe result of the process A?B. Applying a read bias to terminal D 108reads out the result by sensing the state of the ME device.

Patent '656 also states that a separate nonvolatile memory element (forexample, an MTJ) may be incorporated in cell 100. The first time 108 isactivated to read a result, that result also is preferably stored in theseparate ME memory device 122. In the preferred embodiment envisioned in'656, the reconfigurable device is the MFCAD, which normally givesoutput as an electric current. A (current or voltage) bias pulse appliedto terminal E 110 at any time will provide voltage readout at output 112as an alternative to current readout. As discussed in '656, the separatenonvolatile memory element 122 may use a ground 118 that differs fromthe ground 116 used by the reconfigurable logic device. For purposes ofsimplifying and understanding the more important aspects of the presentinvention, less essential features of the device (such as the groundsfor the input are readout functions) are omitted from further discussionherein.

The following paragraphs explain how new forms of HHE devices can beused to form a reconfigurable Boolean logic unit that is operationallyidentical, in all necessary aspects, with the unit formed using theMFCAD. Each of these cells therefore can be used or substituted for suchMFCADs in the architecture developed in '656 as desired for anyparticular application.

A reconfigurable logic cell, using a Hybrid Hall Effect (HHE) device asthe ferromagnetic element, was disclosed in U.S. Pat. No. 6,140,838(incorporated by reference herein). Briefly describing a typicalembodiment, a Hall cross is fabricated using any semiconductor material.A preferred embodiment uses a high mobility semiconductor material suchas a two dimensional electron system (2DES) heterostructure. A thinelectrically insulating layer coats the top of the Hall cross. Twoopposite arms of the cross (for example horizontally opposite, definingthe x-axis) are connected to a readout bias source (voltage or current).The other two arms (for example vertically opposite, defining they-axis) provide an output voltage to a sense circuit. A patterned, thinfilm ferromagnetic element (F) is fabricated on top of the electricallyinsulating layer, with one edge over the center of the Hall cross. Inone common embodiment, the F element is an ellipse or rectangle withaspect ratio of three to one and is oriented with the long axis of theellipse along the horizontal axis of the Hall cross.

The F element is fabricated to have two stable magnetization states,with uniform magnetization along the +/−x-axis. Fringe magnetic fieldfrom the end of F generates a positive or negative Hall voltage measuredalong the y-axis, when bias current I is applied along the horizontalarms. The Hall voltage is linear with current and is identified as+/−DV_(H) or, equivalently, as +/−DR_(H), where DR_(H)=DV_(H)/I. Whenthe Hall cross is fabricated to have a small asymmetry in the positionsof the vertical arms, a small resistance is included in the outputvoltage circuit and the output has discrete levels of 0 (LOW) or+2DV_(H) (HIGH). Input is provided as current pulses applied toinductively coupled integrated write wires. The magnetic field generatedby each current pulse and locally applied to F may flip themagnetization orientation of F between the two stable states.

It can be noted that the physical principles of operation for the HHEmagnetolectronic device are somewhat analogous with those of the MFCAD.There is no spin polarized current in the Hall channel and there is nospin polarized current in the diode channel of the MFCAD. The outputvoltage is generated from an applied magnetic field and a classicalLorentz force exerted on the bias current. Like the integrated MFCAD,the magnetic field is locally applied as the fringe field of a patternedferromagnetic element that has bistable magnetization orientations.These orientations are written with input currents.

A generic representation of a conventional HHE device is shown using thesymbol in FIG. 2A. Rectangle 202 represents a first ferromagneticelement F, and arrow 204 represents a magnetization orientation binarystate (left or right, with fringe fields that correspond with LOW andHIGH output, respectively). An initial orientation (to the left in FIG.2A) for this ferromagnetic element is set with a reset pulse applied toany input terminal. At any time following this, three input currentpulses are applied simultaneously through write wires, grounded at firstground 212, to perform a selected logic operation. As stated above, alocal magnetic field is associated with each current pulse. Thesuperposition of fields from the three separate independent pulses isapplied to ferromagnetic element F 202, potentially causing amagnetization of such element to change orientation in response to suchcombined fields. The prior art HHE device therefore does not use a spinpolarized current to set a state of the ferromagnetic element F.

A first pulse to control terminal C 206 determines the logic function,or operation, of the gate, for example AND or OR. The data input pulses(for the logical operands A, B) are applied to terminals A 208 and B210. The result of the logical process is stored as a magnetizationorientation 204 of ferromagnetic element 202.

At any later time, a pulse applied to Readout bias 214 and grounded at asecond ground terminal 216 provides a bias (voltage or current) imposedacross two opposite arms of the Hall cross (horizontal arms in the aboveparagraph). The Output includes two different possible values, and isexpressed by a floating output voltage, 0 or +2DV_(H), that is madeavailable at Output 218 to a sense circuit. This voltage is suppliedfrom one of the transverse Hall cross arms (a vertical arm in the aboveparagraph). An appropriate ground 216 for the output voltage depends ondetails of the sense circuit, but the opposite Hall cross arm can beused. The current read from the prior art HHE device therefore is alsonot spin polarized.

Patent '838 describes two operational modes of the HHE device, namelylatching and non-latching. The latching mode is appropriate for thenonvolatile logic technique used in the architecture in '656. As seen inFIG. 2A, a typical operation begins with a Reset pulse that sets anorientation M 204 to the left. The Reset pulse preferably has negativeelectric polarity and the associated field is shown pointing to theleft. In a second step, positive polarity current pulses (of zero orunit amplitude) preferably are applied to terminals A, B and C. If thesuperposition of local magnetic fields is sufficient to exceed acharacteristic value of a switching field of ferromagnetic element202—which can be configured by an appropriate selection of materials,geometry, etc.—this causes an orientation 204 to reverse and point tothe right. If the superposition of fields does not exceed the value ofthe switching field of element 202, the orientation 204 remains to theleft.

The result of the Boolean operation is represented as the resultingnonvolatile orientation 204 and can be read out at any desired latertime. An orientation pointing to the left (right) produces voltageV_(Out)=0, binary 0 (V_(out)=2 DR_(H), binary 1). In a typicalembodiment, this operation would be used for Boolean AND or ORoperations. The reset current pulse for HHE 200 in this instance hasnegative polarity. There are several known techniques for providing abipolar power supply on a chip including as developed for commercialMRAM. Therefore there is minimal inconvenience or circuitry associatedwith providing these uniform negative current reset pulses.

To perform NAND and NOR operations, an initial orientation M 204 is setto the right. The resulting fringe field configuration corresponds to aHIGH output value, and a readout performed after initialization wouldgive V_(Out)=2DR_(H). Inputs to in the form of negative current pulsesof sufficient magnitude change the orientation to point to the left. Thefringe field configuration then corresponds to a LOW output value,V_(Out)=0.

Although it may be relatively simple to provide negative reset pulses toany HHE device 200 in a circuit, for any operation, it may not beconvenient to provide negative current inputs at some times and positivecurrent inputs at other times. Similarly, it may not be convenient toprovide negative reset pulses at some times and positive reset pulses atother times.

A modification presented in the '838 addresses this issue. It is wellknown that the write wire can be inverted geometrically, as shown in theright hand side of FIG. 2B. In this case, a positive polarity writepulse (of appropriate magnitude) orients magnetization orientation M 204to the left and a negative polarity pulse orients M to the right. Thisis operationally the same as using the original (non-inverted) writewire structure (left had side of FIG. 2B) with opposite polarity writepulses: in other words, a non-inverted structure with a negative writepulse (signified by the box with “−1” in the left panel) can achieve thesame result as an inverted structure with a positive polarity writepulse (signified by the box with “1” in the right panel).

A more efficient means of controlling (writing) the magnetizationorientation 204 of F 202, and providing inputs to A 208, B 210 and C206, uses a Spin Transfer Torque (STT) write process (Mark Johnson,Wiley Encyclopedia, 2015; and references therein). An HHE device withSTT inputs and which is written using spin polarized current is asignificantly improved device. The STT process is used to setmagnetization states of the patterned F elements in the MFCAD embodimentreferenced in the '266 patent.

A brief review of a general STT process is given here (Mark Johnson,Wiley Encyclopedia, 2015, which is incorporated by reference). To begin,an electric current that is driven across an interface between aferromagnetic metal film (F₁) and a second metal film, eithernonmagnetic (N) or ferromagnetic (F₂), is a spin polarized. This spinpolarized current, J, maintains its polarization in the second metalfilm for a relatively long time. In a qualitative description of the STTprocess, the spin polarized current from a pinned ferromagnetic sourcefilm, F_(p), is driven across an interface and into a second film F_(f)with magnetization orientation that can be altered (freely set or notpinned).

If the spin polarization set in the second film is antiparallel with thealignment of the spin polarized current, the injected electron spinsrelax their orientation. However, spin is a conserved quantity and thusthe spin angular momentum lost by the injected electrons is transferredto some of the localized electrons in F_(f). The injected currentprovides a constant source of spin angular momentum of a single sign andeventually the orientation of spontaneous magnetization M of the secondfilm aligns with that of F_(p). An orientation antiparallel with that ofF_(p) is achieved by reversing the electrical polarity of the spininjected current. This STT process has a quantum efficiency of nearlyunity. A complete STT switching event depends on several factors,including the amplitude and duration of the injected current pulse andoccurs on an approximate time scale of 1-10 nsec.

An HHE device with STT inputs written by a spin polarized current hassignificant advantages over the prior art HHE device that has a singleferromagnetic film that is written using a magnetic field imposed byinductively coupled write wires. A preferred embodiment of the new HHEdevice 250 has a ferromagnetic film F_(f) with STT inputs. The filmF_(f) and components used for the STT process is depicted in FIG. 2C. Athin low transmission barrier 254 is preferably fabricated from anon-magnetic layer (with common materials being aluminum oxide Al2O3,magnesium oxide MgO for tunnel barriers or copper in the case of a metalbarrier) and located between a thin source ferromagnetic film 256, withpinned magnetization orientation 258, and a free ferromagnetic filmF_(f) 260, with an orientation 262 that has at least two bistablestates. Input current pulses 266, 268 and 270 can be applied atterminals A 272, B 274 and C 276, respectively, and grounded at 278.Source ferromagnetic film 254 is preferably sufficiently thin enough sothat its fringe field does not interfere with the fringe field resultingfrom free ferromagnetic field film 260. The combined input current J 280that enters F_(f) 260 is spin polarized and may, for sufficientmagnitude, change an orientation 262. It will be understood by thoseskilled in the art that this is merely one preferred method of impartinga spin polarized current, and that other techniques known or laterdeveloped in the art can be adapted to accomplish the same result fordevice 250.

Summing the input currents, represented by node S 284, may be done usingseparate wires or may be done with more complex techniques apparent tothose skilled in the art in accordance with the goals of the presentdisclosure. Because a completed switch (of the orientation 262) dependsin part on the duration of a pulse, a time-based write technique can usepulses that arrive sequentially (or with some overlap) with a combinedduration of the sequence of pulses chosen to be adequate for a completeswitch. A current pulse of desired magnitude can be delivered by knowntechniques in the art, including choosing appropriate impedance for thewrite wire layers, and in most such cases currents applied to multipleterminals on a single write line will sum because impedances merely addin parallel. Other cases will be apparent to skilled artisans and mayrequire or use a different approach than proposed here, but the preciseimplementation of such schemes is not critical and is believed to beapplication specific. Note that the reset pulse required at thebeginning of any operation can be a single pulse of the appropriatepolarity and amplitude and may be applied to A, B or C.

An improved HHE device having STT input is further shown with theperspective sketch in FIG. 2D. The sketch uses the same approximategeometry depicted for the prior art HHE device in '445. For a writeinput, however, current pulses are summed at node 284, then passedthrough the pinned source layer 256 and into the ferromagnetic layer 260in the form of a spin polarized current. For readout (output), a biascurrent pulse is applied along the Hall cross arms parallel with thex-axis. The output voltage pulse is sensed between the transverse arms,using terminals connected to S1 and S2 as with the prior art approach.

The HHE device in the '838 has output levels of LOW, V˜0V, and HIGH,V=2DV_(H)˜10 to 100 mV for typical Readout bias current I. The HIGHlevel is to sufficient to exceed the gate threshold of somesemiconductor FETs. However, these logic levels are not appropriate forintegration with conventional SDE. Furthermore, the HIGH level is not anoptimal value for providing input current to subsequent devices (tosupport fanout). The output of ˜100 mV is applied to a total resistanceR_(tot) that is the sum of a 50 Ohm impedance line wire plus theresistance of the STT layers. The total resistance is the order 100 to1000 Ohms, and the output current available for STT input varies from0.1 to 1 mA. This may be adequate for providing STT current input for asingle following ME device. However, it's generally not sufficientlylarge to provide fanout to multiple devices in connected stages.Furthermore, the output levels do not have adequate reproducibility forlarge scale integration. For these reasons, the '838 patent described acell that used CMOS FETs to amplify the output.

A new reconfigurable Boolean function unit (BFU) 300, which includes thenew HHE device (FIG. 2D) modified with a capability that inputs can usecurrent pulses and STT, is described in FIG. 3A. This figure shows acell with a parallel interconnected combination of a single HHE device305 and a single inverted HHE device 315. Because of the relatively lowimpedance of ME devices 305, 315, diodes 322 and 324 are used at theoutput of each device, in a preferred embodiment, to prevent dissipationof output voltage through the contiguous device.

In one preferred embodiment, a buffered output 340 using a pair of FETs(an inverter) can easily provide sufficient drive to bring the outputlevels of the HHE BFU to CMOS levels. The implementation of this simpleinverter is not crucial to the invention. Output levels can be set toCMOS levels by buffering the output in a number of well-known ways.

This configuration of two new HHE devices can be used to generate fiveunique (separate) Boolean functions if two separate operation/functioncontrol signals C1 and C2 are implemented, along with two readout biassignals RB1 and RB2. This BFU 300 can thus operate as a NAND, NOR, AND,OR and XOR gate, as described with the table in FIG. 3B (in a manner assimilarly described in '838). The HIGH and LOW outputs at terminal 334are V_(DD) and V_(SS), respectively.

Those skilled in the art will appreciate that it is also possible toobtain an XNOR function through minor modifications to device 300. In apreferred embodiment, an additional inverter 340′ (not shown) wouldfollow inverter 340 with a switch (not shown) between the two. Anadditional third control pulse RB3 is used as well. For the first fivefunctions, RB3 sets the switch to be open and the output is read at 346.For XNOR, RB3 sets the switch to be closed and readout is at an output(not shown) of the second inverter. Other implementations will beapparent to those skilled in the art.

As was noted in '838 this type of device 300 can be implemented as alogical functional building block for higher level processing devices,such as microprocessors, digital signal processors, RISC processors,programmable logic, etc. The expression “logic” device, therefore, asused herein is intended in its broadest connotation and intended toinclude such logical operations, numeric operations, etc. For purposesof simplifying and understanding the more important aspects of thepresent invention, certain less essential features of the device (suchas the grounds for the write wires and for the device itself, the layoutof the write layer and read terminal, etc.) are omitted from furtherdiscussion herein. It will be understood also that specificimplementations of the inventive devices will vary from application toapplication.

It can be seen that the reconfigurable logic cell in FIG. 3A can operateas the ALU in a nonvolatile logic circuit such as described in theaforementioned '656 patent embodiments. As noted above, FIG. 1represents a generic description of a reconfigurable logic cell 100 usedas an ALU. As further explained, this cell includes a separatenonvolatile memory element 122 that provides voltage readout as analternative to current readout. The operation of the cell involves 4steps. As presented in '656, the operational steps in the case of theMFCAD ALU are as follows:

1) Transmitting a functional control or configuration pulse to terminalC 102: this sets the magnetization of the “Control” F element andthereby controls the function of the device, for example to perform oneof several possible Boolean operations. Examples are AND/OR; NAND/NORetc. In this nomenclature, the abbreviation “A?B” represents a chosenoperation.

2) Transmitting input operand or data pulses to input terminal A 104 andinput terminal B 106: these pulses set magnetization states of two Felements that provide local fields to the MFCADs. The configuration oforientations determine the output of the gate.

3) Transmitting a current read pulse to bias terminal D 108: thisapplies a voltage pulse across the diode channel and results in acurrent that depends on the resistance of the channel so that it can beassociated with two different distinguishable current conditions, wherea first current is larger than a second current for example. Thiscurrent in turn, depends on input fields that result from inputs A andB. This “readout” of the results can be done at any time after step (2)and provides a current output. This current also is sent as an input toa magnetic storage element 122, such as an MTJ or a separate magneticfield controlled avalanche diode (MFCAD), in the same cell. Again asalluded to previously, pulses to terminals C, A, B and D may share acommon ground 216. The output current may be sensed by an ammeterbetween terminal 108 and ground 116. Alternatively, the output currentmay be made available at a separate terminal 112.

4) Transmitting a voltage read pulse to bias terminal E 110: thisapplies a voltage pulse to the nonvolatile magnetic storage element 122and the output 112 indicates the stored value. Depending on the type ofmagnetoelectronic device used, the output could be a high or low voltage(using an MTJ) or a high or low current (using an MFCAD). A voltagereadout may be convenient for transmission to an output port, or as avoltage bias to another device. Those skilled in the art will note thatin the first 2 steps, the input pulse is configured as a current pulsebut other circuit considerations may allow the pulse to be defined as avoltage pulse as well.

FIG. 3C represents an ALU 350, suitable for the architecture of '656, inwhich the reconfigurable logic cell is the buffered HHE cell 300 shownin FIG. 3A. This cell operates with the same basic read/writeoperational steps used above to describe the operation of cell 100 inFIG. 1. In one embodiment, this cell also to includes a separatenonvolatile memory element 378.

Following the description of FIG. 3A, the output levels are preferablyCMOS HIGH and LOW levels, V_(DD) and V_(SS). These voltage levels can beconverted to currents, if needed for input to a subsequent ME cell.Depending on particulars and requirements of the circuit, the currentcan be determined by a resistor in a wire that's part of a subsequentstage of the circuit. Alternatively, ALU 350 can have two outputterminals separated by a switch (not shown). One output terminaldelivers the output in the form of different voltage levels. The otherterminal includes a resistor that determines and outputs one of aplurality of different appropriate current levels. In this embodiment, apulse to terminal E 374 sets the switch to select one of the two outputterminals to be output at terminal 376.

The operation of cell 350 now can be compared to the operation of cell100 in FIG. 1:

1) A reset pulse to terminal C1 initializes the magnetizationorientation of the free ferromagnetic film of device 305 (FIG. 3A) topoint left. A reset pulse to terminal C2 initializes the magnetizationorientation of the free ferromagnetic film of device 315 (FIG. 3A) topoint right.

2) Control/configuration and input pulses are applied simultaneously.Separate control configuration pulses are sent to terminals C1 362 andC2 364 in accordance with a desired operation to be performed (FIG. 3B).Data input pulses are sent to terminal A 366 and B 368 for the operands.The A and B input pulses are applied to both devices 305 and 315. Theabbreviation “A?B” represents the chosen operation. Again, referring toFIG. 3B, the operation can be configured to be AND, OR, NAND, NOR orXOR. Application of these pulses sets the magnetization states of thetwo respective F films in devices 305 and 315, according to the chosenBoolean process. The output of gate 350 is now determined based on thecombination of configuration and data input signals.

3) Transmit a pulse to bias terminal E 374 to set the output 376 to be acurrent.

4) Transmit four simultaneous pulses: RB1 to terminal D1 370, RB2 to D2372, a pulse V_(DD) applied to 342 (FIG. 3A), and a pulse V_(SS) appliedto 344 (FIG. 3A). The output of the chosen operation will be a currentpulse at terminal 376, with LOW amplitude I_(OUT)=V_(SS)/R_(W)˜0 (binary0) or HIGH amplitude I_(OUT)=V_(DD)/R_(W) (binary 1). This Readoutprocess can occur at any time after step (2).

5) Transmit a pulse to bias terminal E 374 to set output 376 to be avoltage.

6). Repeat Step (4). The output of the chosen operation will be avoltage pulse at terminal 376, with LOW amplitude V_(OUT)=V_(SS)˜0(binary 0) or HIGH amplitude V_(OUT)=V_(DD) (binary 1).

Using these steps, the nonvolatile logic architecture of '656 can beimplemented using the new reconfigurable HHE device cell 350 (FIG. 3A).This first embodiment has significant advantages as explained below.

First, the output levels are highly reproducible and have largermagnitude than MCFCADs and similar devices. Furthermore, the device canbe reconfigured among five functional choices rather than two. As notedabove, this could be expanded by including additional circuitry.

In addition, there may be applications that demand CMOS output levels,but only require a logic gate that can reconfigure between two choices(AND/OR; NAND/NOR). The simpler structure depicted in FIG. 4A representsa subtype of an ME circuit embodiment that can satisfy theserequirements while using fewer devices than are used in the embodimentof FIG. 3A. In FIG. 4A, an ME circuit embodiment shows an output ofinverted HHE device 410 that is amplified by an inverter 420. In anothersubtype of ME circuit embodiment shown in FIG. 4B, the output of HHEdevice 460 is amplified by buffer amplifier 470.

Those skilled in the art will recognize that each ME cell circuit mayhave advantages in different circuits and applications. As discussedabove, the ground to a Readout bias pulse acts as a reference to an HHEoutput voltage. In the amplifier cells 420 and 470, the voltage appliedto the gate uses reference 414 as ground. As discussed above, the choiceof gate voltage ground, for example source, drain or body forsemiconductor FETs, will vary according to the specific application. Theidea of a composite HHE device cell, as seen in FIGS. 4A and 4B, hasbeen discussed in my prior patent '838 and in other scientificliterature. The present invention uses the improved HHE device (with STTinput) and furthermore shows that these new cells are also appropriatereconfigurable logic units for the ALU shown in FIG. 1. Therefore, thenonvolatile logic architecture described in '656 can be implementedusing these cells.

The present disclosure enables reconfigurable Boolean logic cells thatare based on the improved HHE device. This device (FIG. 2D) has inputcurrent pulses of relatively small magnitude (much smaller than themagnitude required of prior art HHE inputs). The LOW output level isapproximately 0V. Relatively large output levels have been achieved withcompound III-V semiconductor heterostructures, such that a HIGH outputlevel of order 100 mV can be achieved. The composite HHE cells shown inFIGS. 3A, 4A, 4B benefit from a simple structure and CMOS output levels.

As another aspect of the present invention, the nonvolatile logicarchitecture presented in '656 further uses numerous nonvolatileswitches in the sub-circuits and circuits. A nonvolatile switch can bemade using the improved HHE cells described herein along with a singlesemiconductor FET.

One embodiment, shown in FIG. 5, is comprised of an HHE device 510 andan enhancement mode FET 530. The HHE Output 504 is preferably providedto terminal 532 and therefore to a gate 534 of an n-channel enhancementmode FET 530. The Output voltage, with HIGH value typically of 2DV_(H),is defined relative to a read bias ground 802. This same ground can beattached to the source 544, drain 542 or body 546 of the FET 530. Itwill be apparent to those skilled in the art that a variety of choicesfor grounding the gate voltage can be used. Alternatively, the output504 can be treated as a floating voltage and a pull-up or pull-downresistor can be added at terminal 532. When HHE 510 is in a logical lowstate (binary 0), Output=0 V, the n-channel FET is not conducting, andthere is open circuit between terminals S 552 and T 554. When HHE 510 isin a logical high state (binary 1), the voltage at 504 isOutput=+2DV_(H). The magnitude of 2DV_(H) can be the order of 100 mV (orsome other figure suitable for the particular implementation),sufficient to exceed the threshold voltage of an appropriately chosenFET. The n-channel FET 530 then becomes conductive, resulting in a lowresistance connection between terminals S 552 and T 554. Following thisdescription, the circuit of FIG. 5 operates as a nonvolatile switch. Thestate of the switch (open or closed) therefore is determined by thenonvolatile state of HHE device 510. The switch becomes actively open(high impedance) or closed (low impedance) in response to and wheneverbias is applied to readout terminal 506 of HHE device 510.

FIG. 6A shows yet another embodiment of the invention, in which acomposite cell 600 is composed of an HHE device and two FETs in a bufferamplifier 640. In this configuration, cell 600 operates as a nonvolatilememory cell.

The process of storing data (in this case a single bit) takes two steps.In the first step, a Reset current pulse is applied to Input 630. Asdiscussed in prior section in this specification, the Reset may be avoltage pulse, in which case a resistor is chosen to have a value R_(W).The sum R_(tot) of R_(W) plus the resistance of the source film is suchthat the reset voltage applied across R_(tot) results in a currentamplitude I_(W) that is sufficient to set the magnetization orientationof the free film 624. If the input is a current pulse, no seriesresistor is needed.

In the second step, an input write pulse is applied to Input terminal630. For logical/binary 0, the amplitude of the input pulse ispreferably selected to be zero, for either voltage or current inputs.For logical/binary 1, an input current pulse preferably is chosen tohave amplitude I_(W), sufficient to switch a magnetization orientationof free film 624. An input datum voltage pulse is set to have the sameamplitude as a Reset voltage pulse but opposite polarity. The binaryvalue is stored in a nonvolatile way in the form of the final resultingorientation of free film 624.

Readout of the stored value is performed at any desired later time. AReadout bias pulse (typically from a voltage source such as V_(DD)) isapplied from Readout bias terminal 626 to ground 628. Synchronous pulsesof supply voltage V_(DD) 642 and V_(SS) 644 are applied to the n-channeland p-channel FETs, and CMOS level voltage pulses V_(SS) (LOW, binary 0)or V_(DD) (HIGH, binary 1) are produced at the output 652. Pulseduration is not critical, although the external circuit may impose otherconditions.

It will be clear to those skilled in the art that other variations ofcells 620 and 640 may be used to advantage, according to specificdemands of a circuit. Examples include using an inverted HHE cell.Another example is the use of an inverting buffer amplifier for 640. Itis also clear that a separate Reset input terminal may show advantage insome circuits. The requirements of an application may result in oneembodiment being preferred over another.

A circuit symbol for a novolatile memory (NVM) cell 600 is shown in FIG.6B. There may conditions for which a preferred embodiment includes aseparate input terminal 632 for the reset pulse. More generally, thereset pulse may be applied at an input terminal 630.

As noted earlier, the nonvolatile logic architecture presented in '656also employs several nonvolatile memory cells (NV memory). For example,such a cell is used as a test register at the output stage of the ALU,and such cells are used as data registers at the data input/outputports. The nonvolatile memory cell (NVM) described with FIGS. 6A and 6Bis an appropriate memory cell for use in the '656 architecture where itcan be integrated with other ME devices of like materials, functionalityand peripheral (I/O signal generation) requirements.

As another aspect of the present invention, nonvolatile memory cell 600can be used with advantage in simple traditional semiconductortechnology (such as CMOS) sub-circuits and circuits. A simple embodimentof a magnetoelectronic/semiconductor adder circuit is shown in FIG. 7.This figure schematically shows a Half Adder sub-circuit 1000 using acombination of CMOS AND, OR and NOT gates. The Half Adder 700 is drivenby a conventional clock circuit (not shown). Synchronized input pulsesare applied at terminals A 710 and B 712. The output is a SUM bit (0or 1) and a CARRY bit (0 or 1) that appear synchronously at terminals716 and 714, respectively.

In normal operation, the output values are passed to inputs of otherlogic sub-circuits. Alternatively, the values may be sent to a temporarymemory register that stores the values until they are needed, typicallya few clock cycles later.

There may be occasions when the SUM and CARRY bits are not needed untila later time, that is, for thousands or millions of clock cycles. Theremay be other occasions when the output bits are needed at a much latertime (seconds, hours or even longer). Nonvolatile memory cells 730 and740 can be added to the Half Adder circuit, as shown in FIG. 10, toprovide nonvolatile storage of the SUM and CARRY bit values. The HalfAdder 1000 can be powered down until it is needed again. The values ofthe SUM and CARRY bits can be provided to another sector of the circuit,in the form of CMOS pulses, by applying voltage pulses to cells 730 and740 in the manner described above.

During operation of the Half Adder cell 1000, reset pulses are sent tothe two cells 730 and 740 during a first clock pulse. The next clockpulse applies simultaneous input pulses to A 710 and B 712. When outputCARRY pulse reaches 714, that pulse is also applied as input to NVM 730and simultaneous supply pulses are applied to NVM 730. When the outputSUM pulse reaches 716, that pulse is also applied as input to NVM 1040and simultaneous supply pulses are applied to NVM 1040. At any latertime, the stored SUM and CARRY values are available at 716 and 722,respectively, and are supplied to subsequent circuits by applyingReadout bias and supply (V_(DD) and V_(SS)) pulses to these two NVMcells.

While this is a relatively simple example using a low level sub-circuit,NVM cells can be added to other types of CMOS sub-circuits and circuitsof greater complexity for similar purposes. At a higher level, NVM cellscan be added to a sector of circuits in a processing chip, to store anydesired number of data values that result from ongoing computations.This can be valuable if other portions of the chip are not ready toreceive these values. The computing sector that generated the data canbe powered down until it is needed again. The values that resulted fromthe computation of that sector are available to other portions of thechip at any time.

The examples above are merely illustrative of the general principles toinherent in the teaching of the present invention. Other variations willbe apparent to skilled artisans, and the present invention is by nomeans restricted to such embodiments and examples.

What is claimed is:
 1. A hybrid Hall Effect magnetoelectronic devicewhich is configurable into different device states comprising: a Hallcross element; a first ferromagnetic film situated on said Hall Crosselement and having a configurable magnetization orientation representinga device state; a second ferromagnetic film having a pinnedmagnetization orientation; a barrier film situated between said firstferromagnetic film and second ferromagnetic film and configured toconduct and impart a spin-torque transfer current to set the devicestate for said configurable magnetization orientation in io said firstferromagnetic film.
 2. The device of claim 1 further including a groundcoupled to said first ferromagnetic film.
 3. The device of claim 1wherein said first ferromagnetic film magnetization orientation has atleast two bistable states.
 4. The device of claim 1 wherein said barrierlayer is comprised of aluminum oxide or magnesium oxide.
 5. The deviceof claim 1 further including a first data input, a second data input,and a configuration input coupled to a summing node and said secondferromagnetic film.
 6. The device of claim 4 wherein the device performsboth AND/OR functions when said first ferromagnetic film has a firstinitial state, and the device performs both NAND/NOR function when saidfirst ferromagnetic film has a second initial state.
 7. The device ofclaim 1 wherein the device state can be read by detecting an electricalsignal across said Hall cross element that is related to a fringe fieldimparted by said first ferromagnetic film acting on an electricalcurrent flowing in said Hall cross element.
 8. The device of claim 1further including a CMOS inverter coupled to an output of the device. 9.The device of claim 1 further including a CMOS amplifier coupled to anoutput of the device.
 10. The device of claim 1 wherein the device has alogical low output value of approximately 0 volts.
 11. The device ofclaim 1 wherein the device is configured and integrated withsemiconductor components in a first region of an integrated circuit aspart of a non-volatile switch.
 12. The device of claim 1 wherein thedevice is configured and integrated with semiconductor components in afirst region of an integrated circuit as part of a non-volatile memorycell.
 13. The device of claim 12 wherein the device is self-containedand not part of a non-volatile memory cell array.
 14. The device ofclaim 1 wherein the device is configured and integrated withsemiconductor components in a first region of an integrated circuit aspart of a logic circuit.
 15. The device of claim 14 wherein each logicgate in said logic circuit includes an integrated non-volatile memorycell.
 16. The circuit of claim 14 wherein the logic circuit is ahalf-adder circuit and said device stores a result of a carry or sumoperation.
 17. An integrated magnetoelectronic and semiconductor circuitsituated on a common integrated circuit substrate comprising: amagnetoelectronic device situated in a first portion of the integratedcircuit substrate and including: a Hall cross element; a firstferromagnetic film situated on said Hall Cross element and having aconfigurable magnetization orientation representing a device state; asecond ferromagnetic film having a pinned magnetization orientationorientation; io a barrier film situated between said first ferromagneticfilm and second ferromagnetic film and configured to conduct and imparta spin-torque transfer current to set a device state for saidconfigurable magnetization orientation in said first ferromagnetic film;an output for reading the device state for the magnetoelectronic device;a semiconductor device with an input connected to said output and alsosituated in a first portion of the integrated circuit substrate; whereinthe integrated magnetoelectronic and semiconductor circuit areconfigured as one of a non-volatile switch, memory element, and logicgate.
 18. A hybrid Hall Effect device comprising: a conductive filmlayer having a top surface and capable of carrying an electricalcurrent; a first ferromagnetic film having a configurable magnetizationorientation, and covering a first portion of the top surface, and not asecond portion, such that a fringe magnetic field substantially normalto such surface can be generated by an edge portion of the ferromagneticfilm; and a second ferromagnetic film having a pinned magnetizationorientation io orientation; a barrier film situated between said firstferromagnetic film and second ferromagnetic film and configured toconduct and impart a spin-torque transfer current to set a state forsaid configurable magnetization orientation in said first ferromagneticfilm; wherein an electrical signal can be generated in response to thefringe magnetic field acting on the electrical current in the conductivefilm layer.
 19. A method of operating a hybrid Hall Effect deviceincluding a Hall Effect element and a first ferromagnetic film having aconfigurable magnetization orientation representing a device state,comprising: providing a second ferromagnetic film having a pinnedmagnetization orientation orientation; providing a spin polarizedcurrent through said second ferromagnetic film to the firstferromagnetic film using spin torque transfer; wherein said spinpolarized current is selected and controlled to alter a device state forsaid configurable magnetization orientation in said first ferromagneticfilm.
 20. The method of claim 19 including a step: reading a devicestate by detecting an electrical signal generated in response to afringe magnetic field acting on an electrical current in the conductivefilm layer.
 21. The method of claim 19 including a step: providing areset pulse to reset a state of the device.
 22. The method of claim 19wherein the hybrid Hall Effect device is integrated with a semiconductorFET as a non-volatile logic gate which operates without a clock and onlyconsumes power through read/write pulses applied to such gate.